Surface condenser



March 26, 1935. w. M. NAGLE SURFACE CONDE NSER Filed Dec. 11, 1933Patented Mar. 26, 1935 UNITED STATES PATENT OFFICE 18 Claims.

This invention relates to heat interchange apparatus, such as surfacecondensers, in which vapor is condensed by the transfer of heat to acooling fluid through a wall interposed there between. It is the objectof the invention to improve the efficiency of such apparatus.

In apparatus of this general character the vapor condenses upon the wallwhich separates it from the cooling fluid and wets the wall so that athick layer of condensate always is present upon the condensing surface,that is, the surface of the wall adjacent the vapor, This thick layer ofcondensate insulates the condensing surface and seriously limits thecondensing capacity of. the apparatus, namely, limits the amount ofvapor that may be condensed per unit time with a unit area of condensingsurface and with a given difference in temperature between the vapor andthe cooling fluid.

The present invention contemplates a method of treating the condensingsurface of apparatus of this general type to modify the condensingsurface substantially permanently so that it is not wetted by thecondensate and so that the latter is caused to gather together in theform of drops on the condensing surface, leaving a substantial fractionof the condensing surface directly exposed to the vapor andavailable foreffecting heat transfer at a maximum rate. Thus, the condensing surfaceis treated to leave a thin film of an agent which has the ability tocling tenaciously to the condensing surface and not be washed away bythe normal action of the vapor or its condensate and which is non-wet--table by the condensate. The treating agent is used in such quantity asto form an extremely thin adsorbed film upon the condensing surface soas not to introduce a substantial additional thermal resistance. Thedrop-wise condensation efiected in accordance with the inventionincreases several times the individual coefficient of heat transfer fromcondensing steam to a solid surface expressed as the quantity of heattransfer per unit time per unit surface area. per unitdifierence intemperature between and the condensing surface.

It has been discovered that agents containing compounds having one ormore non-polar parts or hydrocarbon radicals attached to an active polargroup are capable of promoting lasting drop-wise condensation of steamwhen the compound is applied on' metals of moderate smoothness. Thepolar group of these compounds probably causes the compound to adsorb onthe 55 surface of the metal or form an insoluble comthe steam pound withthe metal while. the hydrocarbon group probably serves to render themetal surface non-wettable to water. Entirely non-polar compounds, suchas the parafiin hydrocarbons, do not cling tenaciously to the surface ofthe metal and, consequently, are not suited for promoting drop-wisecondensation. The higher fatty acids, such as'oleic, stearic andpalmitic acids, are well suited for promoting lasting drop-Wisecondensation of steam on moderately .smooth tubes of copper, brass,admiralty metal, Monel metal, nickel and chrome-nickel steels. Fats andwaxes which contain the higher fatty acids may also be used. Organiccompounds containing bivalent sulphur, such as the xanthates,dithiophosphates and mercaptans,. are well suited for promotingdrop-wise condensation of steam on copper and copper alloys, such asbrass and Monel metal. Particularly. good results have been obtainedwith potassium amyl, xan thates, potassium ethyl xanthates, amylmercaptans and benzyl mercaptans. In general, those compounds of theclasses of organic compounds above mentioned which contain the so-calledlarger hydrocarbon radicals are more effective in promoting drop-wisecondensation than those which contain the smaller hydrocarbon radicals.

The treating agent may be applied by rubbing the condensing surface witha cloth moistened with the agent or with a solution of the agent in asuitable solvent or by introducing the agent or its solution into thesteam chamber as a spray or vapor. The agent may be applied by washingthe steam chamber with a solution or an emulsion of the treating agent.If the condensing surface is rough it should be made moderately smoothby grinding or bufiing. The treating agent may be applied subsequent tothe smoothing operation or the two operations may be combined by mixingthe treating agent with the abrasive.

The single figure of the accompanying drawing is a detail fragmentarysectional view of one wall of a surface condenser which separates thevapor to be condensed and the cooling fluid. As illustrated, the surfaceof the wall 10 adjacent the vapor to be condensed is providedwith anadsorbed film 11 of any one of the treating agents above mentioned. Itwill be noted that the film 11 is united to the surface of the wall 10by a bond, 'as indicated at 12, which probably is brought about by aunion between the treating agent and the metal to form an insolublecompound. The vapor to be condensedcondenses upon the surface of thefilm 11 inthe form of drops 13 which roll off without wetting the film11 and leave numerous areas 14 directly exposed to the vapor.

The following is illustrative of the advantages of the invention. Whencondensing saturated steam on a clean nickel tube in a small fallingfilm condenser the over-all coeflicient of heat transmission was foundto be 456 B. t. u. per square foot, per hour per degree Fahrenheitdifference between the temperatures of the steam and the cooling waterbut when the tube was treated with oleic acid drop-wise condensationresulted and the over-all rate of heat transfer rose to 950. Had thethermal resistance through the tube and on the cooling water side of thetube been less than what was employed, the gain in condensing efiiciencywould have been even more striking.

Using an apparatus treated in accordance with the invention I havesecured drop-wise condensation of steam at thermal current densitiesmany fold that obtained in a typical surface condenser in a power plant.In the above example, the thermal current density was 135,000 Britishthermal units per hour per square foot of condensing surface.

I claim: v

1. The method of improving the condensing efficiency of heat interchangeapparatus in which vapors are condensed by the transfer of heat to acooling fluid through a wall interposed therebetween which comprisesforming upon the surface of said wall with which the vapors contact afilm of a material which has the property of tenaciously resistingremoval by the normal action of said vapor and its condensate and isnon-wettable by said condensate. y

2. The method of improving the condensing efficiency of heat interchangeapparatus in which steam is condensed bythe transfer of heat to acooling fluid through a wall interposed therebetween which comprisesforming upon the surface of said wall with which the steam contacts afilm of an organic compound having a non-polar part attached to a polarpart and capable of clinging tenaciously to said surface and which isnonwettable by water.

3. The method of improving the condensing efllciency of heat interchangeapparatus in which steam is condensed by the transfer of heat to acooling fluid through a wall interposed therebetween which comprisesforming upon the surface of said wall with which the steam contacts afilm of a compound selected from the group which consists of fatty acidsand organic compounds containing bivalent sulphur, said compoundcontaining a non-polar part and a polar part.

4. The method of improving the condensing efficiency of heat interchangeapparatus in which steam is condensed by the transfer of heat to acooling fluid through a wall interposed therebetween which comprisesforming upon the surface of said wall with which the steam contacts afilm of a fatty acid.

5. The method of improving the condensing efliciency of heat interchangeapparatus in which steam is condensed by the transfer of heat to acooling fluid through a wall interposed therebetween which comprisesforming upon the surface of said wall with which the steam contacts afilm of a dithiophosphate.

6. The method of improving the condensing efficiency of heat interchangeapparatus in which steam is condensed by the transfer of heat to acooling fluid through a wall interposed therebetween which comprisesforming upon the surface of said wall with which the steam contacts afilm of a mercaptan.

7. A heat interchange apparatus in whicl i vapor is condensed by thetransfer of heat'to a cooling fluid through a wall interposedtherebetween wherein the surface of said wall upon which said vaporcondenses has a thin adsorbed film of a material which clingstenaciously to the wall and resists removal by the normal action of saidvapor and its condensate and is nonwettable by said condensate. i

8. A heat interchange apparatus in which steam is condensed by thetransfer of heat to a cooling fluid through a wall interposedtherebetween wherein the surface of said wall upon which said steamcondenses has a thin adsorbed film of an organic compound having anon-polar part attached to a polar partand capable of clingingtenaciously to said surface and which is nonwettable by water.

9. A heat interchange apparatus in which steam is condensed by thetransfer of heat to a cooling fluid through a wall interposedtherebetween wherein the surface of said wall upon which said steamcondenses has a thin adsorbed film of a compound selected from the groupwhich consists of fatty acids and organic compounds containing bivalentsulphur, said compound con-1 taining a non-polar part and a polar part.

10. A heat interchange apparatus in which steam is condensed by thetransfer of heat to a cooling fluid through a wall interposedtherebetween wherein the surface of said wall upon which said steamcondenses has a thin adsorbed film of a fatty acid.

11. A heat interchange apparatus in which steam is condensed by thetransfer of heat to a cooling fluid through a wall interposedtherebetween wherein the surface of said wall upon which said steamcondenses has a thin adsorbed film of a dithiophosphate.

12. A heat interchange apparatus in which steam is condensed by thetransfer of heat to a cooling fluid through a wall interposedtherebetween wherein the surface of said wall upon which said steamcondenses has a thin adsorbed film of a mercaptan.

13. The method of improving the condensing efficiency of heatinterchange apparatus in which steam is condensed bythe transfer of heatto a cooling fluid through a wall interposed therebetween whichcomprises forming upon the surface of said wall with which the steamcontacts a film of a compound selected from the group which consists ofthe higher fatty acids and organic compounds containing bivalentsulphur, said compound containing a non-polar part and a polar part.

14. The method of improving the condensing 'eificiency of heatinterchange apparatus in which compound containing a non-polar part anda polar part.

16. A heat interchange apparatus in which steam is condensed by thetransfer of heat to a cooling fiuid through a wall interposedtherebetween wherein the surface of said wall upon which said steamcondenses has a thin adsorbed film of a higher fatty acid.

17. The method of improving the condensing efiiciency of heatinterchangeapparatus in which steam is condensed by the transfer of heat to acooling fluid through a wall interposed therebetween which comprisesforming upon the surface of said wall with which the steam contacts afilm of an organic compound containing bivalent sulphur, said compoundcontaining a nonpolar' part and a polar part.

18. A heat interchange apparatus in which steam is condensed by thetransfer of heat to a cooling fluid through a wall interposedtherebetween wherein the surface of said wall upon which said steamcondenses has a thin adsorbed film of an organic compound containingbivalent sulphur, said compound'containing a non-polar part and a polarpart.

WESLEY M. NAGLE.

